The Dirty Dozen and Clean 15 lists help consumers choose produce with lower levels of pesticides

The Environmental Working Group's 2014 list of produce with the most pesticide residue. (EWG)

The U.S.-based Environmental Working Group has released its "Dirty Dozen" and "Clean 15" lists for 2014, detailing which fruits and vegetables have the most — and least — pesticide residue.

The EWG is a non-profit organization that acts as a public health and environmental watchdog, monitoring consumer products, food and environmental practices.

Senior analyst Sonya Lunder said the organization has been looking at the safety of pesticides on fruits and vegetables for over a decade, based on data gathered by the U.S. Department of Agriculture and Food and Drug Administration.

But the information "wasn’t formatted in a way people without a scientific degree or courses in statistics could really take any conclusions away from,” she said.

That's when the lists started. And though they do not change greatly year over year, each list brings to light certain new points of interest.

This year's data found that a single, conventionally grown grape sample contained 15 pesticides, and an average potato had more pesticides by weight than any other food tested.

Cauliflower, sweet potatoes and avocado among the EWG's Clean 15 list for 2014. (EWG)This year's Dirty Dozen list includes apples, strawberries, grapes and celery — produce that is often eaten unpeeled. While the Clean 15 singles out avocado, sweet corn, pineapple, cabbage and others that often have a protective outer layer.

This year the EWG added an extra category — the Dirty Dozen Plus — to include kale and collard greens. The vegetables don’t meet the group's traditional ranking criteria, but were still found to have residues of pesticides it considers toxic.

“This is the fourth year where we’ve had apples on the top of the Dirty Dozen list," Lunder said. "Meaning they have the most pesticides and the highest concentrations on them.”

In addition to being sold in the produce section, those are the same apples that are processed into baby food and pressed into apple juice. Many are also exported to China, Mexico and Canada.

Lunder said the EWG discovered a common pesticide on American apples that’s banned in the European Union because of safety concerns. Diphenylamine is applied after apples are harvested to protect the peel from breaking down during storage. It has been linked to nitrosamines, which are "well-known and well-studied cancer-causing chemicals that are found and formed in smoked meats and other consumer products,” Lunder explained.

“Now in the most recent year of sampling, we found this on 80 per cent of American apples and [in a] lower concentration and less frequently in apple sauce,” she said.

A separate study published at the end of April in the journal Environmental Research by the Royal Melbourne Institute of Technology in Australia looked at pesticide levels in organic food.

In it, 13 adults were divided into two groups. One ate conventional food for a week, while the other consumed about 80 per cent organic food. Then the groups switched and ate the alternate diet. The study found that when tested on the eighth day of each phase, those in the organic group had reduced pesticide levels in their urine by 89 per cent.

Lunder says studying the levels of pesticides in produce has motivated her to make changes in her own home, including swapping conventional for organic raisins.

“Because that's a time you may sit down and eat a lot of raisins and you’re getting all the pesticides that would be found on grapes individually,” she said.

Lunder said the American Academy of Pediatrics, which takes a broad look at children’s health and safety, has also endorsed the work being done by the EWG.

Citing research that links childhood exposure to pesticides with behavioural problems, decreased cognitive function and pediatric cancers, the AAP has recommended parents take steps to reduce pesticide exposure in the home, which includes using lists like the Dirty Dozen and Clean 15 in the produce aisle.